Generating and processing multi-user data units for WLAN

1. A method for generating a multi-user data unit for transmission via a multiple input, multiple output (MIMO) communication channel, the method comprising: generating, at a communication device, a multi-user data unit having a preamble and a data portion, wherein the preamble of the multi-user data unit includes a plurality of training sequences, a first field, and a second field, wherein the preamble of the multi-user data unit is structured such that i) the first field of the preamble precedes the plurality of training sequences, and ii) the plurality of training sequences precedes the second field of the preamble, wherein the plurality of training sequences are to be used by multiple receivers for channel estimation, wherein the first field of the preamble includes a plurality of indications of respective numbers of spatial or space-time streams for respective receivers of the multiple receivers to enable each respective receiver of the multiple receivers to determine a respective set of one or more training sequences, in the plurality of training sequences, that corresponds to the respective receiver, wherein the second field of the preamble includes respective modulation and coding scheme information for the respective receivers of the multiple receivers, and wherein the data portion of the multi-user data unit is to be transmitted using respective modulation and coding schemes for the respective receivers of the multiple receivers; and transmitting, with the communication device, the multi-user data unit.

2. The method of claim 1 , wherein the plurality of indications of respective numbers of spatial or space-time streams are ordered according to an order.

3. The method of claim 2 , further comprising: generating, at the communication device, another data unit that includes information indicating the order, wherein the other data unit is to be transmitted prior to the first field of the preamble.

4. The method of claim 1 , wherein transmitting the multi-user data unit comprises: transmitting, with the communication device, the first field of the preamble in an omni-directional mode; and respectively beam-steering, with the communication device, the second field of the preamble to the respective receivers of the multiple receivers.

5. The method of claim 4 , wherein transmitting the multi-user data unit further comprises: respectively beam-steering, with the communication device, respective sets of one or more training sequences to the respective receivers of the multiple receivers.

6. The method of claim 1 , wherein a first sub-field of the first field of the preamble includes a first indicator of a first set of one or more training sequences that corresponds to a first receiver of the multiple receivers; wherein a second sub-field of the first field of the preamble includes a second indicator of a second set of one or more training sequences that corresponds to a second receiver of the multiple receivers.

7. An apparatus, comprising: a wireless network interface device having one or more integrated circuits, wherein the wireless network interface device is configured to: generate a multi-user data unit having a preamble and a data portion, wherein the preamble of the multi-user data unit includes a plurality of training sequences, a first field, and a second field, wherein the preamble of the multi-user data unit is structured such that i) the first field of the preamble precedes the plurality of training sequences, and ii) the plurality of training sequences precedes the second field of the preamble, wherein the plurality of training sequences are to be used by multiple receivers for channel estimation, wherein the first field of the preamble includes a plurality of indications of respective numbers of spatial or space-time streams for respective receivers of the multiple receivers to enable each respective receiver of the multiple receivers to determine a respective set of one or more training sequences, in the plurality of training sequences, that corresponds to the respective receiver, wherein the second field of the preamble includes respective modulation and coding scheme information for the respective receivers of the multiple receivers, and wherein the data portion of the multi-user data unit is to be transmitted using respective modulation and coding schemes for the respective receivers of the multiple receivers; and transmit the multi-user data unit.

8. The apparatus of claim 7 , wherein the plurality of indications of respective numbers of spatial or space-time streams are ordered according to an order.

9. The apparatus of claim 8 , wherein the wireless network interface device is further configured to: generate another data unit that includes information indicating the order, wherein the other data unit is to be transmitted prior to the first field of the preamble.

10. The apparatus of claim 7 , wherein the wireless network interface device is further configured to: transmit the first field of the preamble in an omni-directional mode; and respectively beam-steer the second field of the preamble to the respective receivers of the multiple receivers.

11. The apparatus of claim 10 , wherein the wireless network interface device is further configured to respectively beam-steer respective sets of one or more training sequences to the respective receivers of the multiple receivers.

12. The apparatus of claim 7 , wherein a first sub-field of the first field of the preamble includes a first indicator of a first set of one or more training sequences that corresponds to a first receiver of the multiple receivers; wherein a second sub-field of the first field of the preamble includes a second indicator of a second set of one or more training sequences that corresponds to a second receiver of the multiple receivers.

13. A method for processing a multi-user data unit received via a multiple input, multiple output (MIMO) communication channel, the method comprising: receiving, at a communication device, a multi-user data unit having a preamble and a data portion, wherein the preamble of the multi-user data unit includes a plurality of training sequences, a first field, and a second field, wherein the preamble of the multi-user data unit is structured such that i) the first field of the preamble precedes the plurality of training sequences, and ii) the plurality of training sequences precedes the second field of the preamble, wherein the plurality of training sequences corresponds to multiple receivers, wherein the communication device is one of the multiple receivers, wherein the first field of the preamble includes a plurality of indications of respective numbers of spatial or space-time streams for respective receivers of the multiple receivers to enable each respective receiver of the multiple receivers to determine a respective set of one or more training sequences, in the plurality of training sequences, that corresponds to the respective receiver, and wherein the second field of the preamble includes respective modulation and coding scheme information for the respective receivers of the multiple receivers; processing, at the communication device, the first field of the preamble to determine a respective set of one or more training sequences which corresponds to the communication device; generating, at the communication device, a channel estimate during the determined set of one or more training sequences which corresponds to the communication device; using the channel estimate to process, at the communication device, the second field of the preamble; and using, at the communication device, a modulation and coding scheme intended for the communication device based on the second field to process the data portion of the multi-user data unit.

14. The method of claim 13 , further comprising: using, at the communication device, training sequences among the plurality of training sequences other than the determined set of one or more training sequences which corresponds to the communication device to mitigate interference resulting from spatial or space-time streams to other receivers of the multiple receivers when processing the second field of the preamble.

15. The method of claim 13 , wherein one of the plurality of indications is determined as corresponding to the communication device based on an ordering.

16. The method of claim 15 , further comprising: receiving, at the communication device, another data unit that includes ordering information, wherein the other data unit is received prior to receiving the first field of the preamble; and determining, at the communication device, the ordering using the ordering information.

17. An apparatus, comprising: a wireless network interface device associated with a communication device, the wireless network interface device having one or more integrated circuits, wherein the wireless network interface device is configured to: receive a multi-user data unit having a preamble and a data portion, wherein the preamble of the multi-user data unit includes a plurality of training sequences, a first field, and a second field, wherein the preamble of the multi-user data unit is structured such that i) the first field of the preamble precedes the plurality of training sequences, and ii) the plurality of training sequences precedes the second field of the preamble, wherein the plurality of training sequences corresponds to multiple receivers, wherein the communication device is one of the multiple receivers, wherein the first field of the preamble includes a plurality of indications of respective numbers of spatial or space-time streams for respective receivers of the multiple receivers to enable each respective receiver of the multiple receivers to determine a respective set of one or more training sequences, in the plurality of training sequences, that corresponds to the respective receiver, wherein the second field of the preamble includes respective modulation and coding scheme information for the respective receivers of the multiple receivers; process the first field of the preamble to determine a respective set of one or more training sequences which corresponds to the communication device; generate a channel estimate using the determined set of one or more training sequences which corresponds to the communication device; use the channel estimate to process the second field of the preamble; and use a modulation and coding scheme intended for the communication device based on the second field to process the data portion of the multi-user data unit.

18. The apparatus of claim 17 , wherein the wireless network interface device is further configured to: use training sequences among the plurality of training sequences, other than the determined set of one or more training sequences which corresponds to the communication device to mitigate interference resulting from spatial or space-time streams to other receivers of the multiple receivers when processing the second field of the preamble.

19. The apparatus of claim 17 , wherein the wireless network interface device is further configured to: determine that one of the plurality of indications corresponds to the communication device based on an ordering.

20. The apparatus of claim 19 , wherein the wireless network interface device is further configured to: determine the ordering using ordering information provided in another data unit that is received prior to receiving the first field of the preamble.